This invention pertains generally to analog to digital converters and more particularly to analog to digital converters of the quantized feedback or charge balancing type.
In analog to digital converters of the quantized feedback or charge balancing type, the analog input signal is integrated and charge is applied to the integrating capacitor in predetermined measured quantities to offset or balance the input signal. A counter is incremented and decremented in accordance with the balancing current to provide a count corresponding to the input signal. This type of system has a definite advantage over conventional dual slope systems in that the integrator can have a relatively high voltage slew rate even with small input voltages. The amount of charge to be added or subtracted is determined by monitoring the integrator output, and the high slew rate increases the accuracy of the charge balancing and the output count.
With quantized feedback techniques of the prior art, it has been possible to provide resonable conversion accuracy only with amplifiers having relatively low offset voltages. Heretofore, such amplifiers have been provided by utilizing discrete components or by using separate integrated circuits for the analog and digital portions of the system, and it has not been possible to build a satisfactory quantized feedback converter on a single chip.